1. Field of the Invention
The present invention relates to a vehicle such as a riding lawn mower, provided with a transaxle apparatus supporting an axle to which wheels are attached. More particularly, it relates to a structure of the transaxle apparatus, and a structure for drivingly connecting front and rear transaxle apparatuses in the vehicle to each other.
2. Related Art
Conventionally, there is a well-known articulate riding lawn mower with a pivotally connected first frame and second frame so as to allow the second frame to be folded relative to the first frame. The first frame is equipped with an engine and a transaxle apparatus supporting an axle driven by the engine. The second frame is equipped with a working device such as a mower device, a driver's unit, and an axle casing supporting a freely rotatable axle. Furthermore, a riding lawn mower provided with an Ackerman type steering system is also well known.
For example, the Japanese Patent Laid Open Gazette 2000-270,651 discloses an articulate four-wheeled lawn mower in which the first frame serves as a rear frame and the second frame serves as a front frame. The rear frame is provided with an HST (a hydrostatic transmission) for transmitting engine power to rear wheels supported by the rear frame. Also, the rear frame is provided with a power take-off shaft for taking out power from a pump shaft of a hydraulic pump of the HST so as to transmit the rotation of the power take-off shaft to a mower device supported by the front frame.
The vehicle of such conventional structure is a so called two-wheel drive vehicle, wherein, while the axle supported by the first frame usually disposed rearward is driven by the engine, the axle supported by the axle casing of the second frame usually disposed forward idles regardless of the power for driving the axle of the first frame.
However, the two-wheel drive vehicle, which drives only rear wheels, is disadvantageous in gradeability on a slope and roadability on a bad road. The vehicle, when being bogged in mud etc., cannot escape easily. Thus, in order to resolve the problem, the vehicle is desirably made into a four-wheel drive type, which drives both rear and front wheels.
As a conceivable manner for solving the problem, a four-wheel drive articulate vehicle may be provided. However, in the above-disclosed vehicle including the rear frame on which the engine and the power take-off shaft are mounted, the power take-off shaft is rotated synchronously to rotation of the pump shaft so that the rotary speed of the power take-off shaft is constant as long as the rotary speed of the engine is constant, while the rotary speed of the rear wheels driven by output of the hydraulic motor is changed by speed change operation for adjusting a swash plate angle of the hydraulic pump. Thus, the power take-off shaft for driving the working device cannot be used as a front-wheel drive shaft simply. Even if another power take-off shaft is allowed to be provided in the transaxle apparatus on the rear frame so as to take out output power of the HST and to drive the front wheels synchronously to the rear wheels, there is considerable limitation in arrangement of a mechanical transmission system between the transaxle apparatuses on the front and rear frames because it is necessary to ensure the rotatability of both the frames and to arrange the transmission system for driving the working device in the place. The four-wheel drive articulate vehicle disclosed by U.S. Pat. No. 6,425,452, in which both the transaxle apparatuses on the respective first and second frames incorporate respective HSTs, is very expensive and requires both the HSTs to be controlled synchronously.